As shown in FIG. 14, it is conventionally known that a hollow housing (container) (PA1) is formed by joining first and second halves (PA1a and PA1b) together so as to form a single one (e.g., Japanese Patent Application Publication Number H10-23563 issued Jan. 23, 1998). In this figure, fit projection parts (PA2) stuck out of the first half (PA1a) are fit in fit grooves (PA4) made in the second half (PA1b), respectively. Specifically, nails (PA7) are respectively stuck out in the outward directions of the long sides of the first half (1a) from the tips of the fit projection parts (PA2). The nails (PA7) are engaged with nail holders (recesses) (PA8) provided for the fit grooves (PA4), respectively, when the fit projection parts (PA2) are fit in the fit grooves (PA4).
Thus, the nails (PA7) and the nail holders (PA8) engaged with each other are used for the fit structure of the housing (PA1). In addition, in order to easily insert the fit projection parts (PA2) into the fit grooves (PA4), each fit groove (PA4) is formed into such a shallow groove as the only tip of a corresponding fit projection part (PA2) is fit in itself. However, when the housing (PA1) receives impact, any of the fit projection parts (PA2) may come off from a corresponding fit groove(s) (PA4) by bounce of the impact. In this case, the housing (PA1) can be easily broken down into the first and second halves (PA1a and PA1b). Specifically, a load may be added to the first half (PA1a) in the inward and outward direction of the housing (PA1), i.e., in the opposite direction of the insertion direction of the nails (PA7) into the nail holders (PA8) in one side as shown in the arrow “G”. In this instance, deformation and bending of each tip of the fit projection parts in the one side becomes larger than that of each tip of the fit projection parts in the opposite side. Accordingly, since the nails (PA8) of the fit projection parts (PA2) in the one side can easily come off from the corresponding nail holders (PA8), fit structure of the fit projection parts and the fit grooves in the housing can easily come off.
Further expanding on the above, the internal walls of some fit grooves (PA4) are end faces of elastic pieces (free ends) (PA20) which can elastically deform in the directions of the arrows “J1” and “J2”. When the corresponding fit projection parts (PA2) are inserted into the fit grooves (PA4), the elastic pieces (PA20) are pushed by the fit projection parts (PA2) to elastically deform, and accordingly the widths of the fit grooves are be spread. Thereby, the fit projection parts can be easily engaged with the fit grooves. However, in case a load is added to the first half (PA1a) as stated above, the elastic pieces (PA20) are pushed by the tips of the corresponding fit projection parts (PA2) largely deformed and then bent by the load, and accordingly elastically deform. As a result, the widths of the corresponding fit grooves (PA4) are spread. Therefore, fit structure of the fit projection parts and fit grooves in the housing can easily come off.